Coated Fullerenes, Compositions And Dielectrics Made Therefrom

ABSTRACT

The present invention relates to coated fullerenes comprising a layer of at least one inorganic material covering at least a portion of at least one surface of a fullerene and methods for making. The present invention further relates to composites comprising the coated fullerenes of the present invention and further comprising polymers, ceramics, and/or inorganic oxides. A coated fullerene interconnect device where at least two fullerenes are contacting each other to form a spontaneous interconnect is also disclosed as well as methods of making. In addition, dielectric films comprising the coated fullerenes of the present invention and methods of making are further disclosed.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to coated fullerenes comprising a layer ofat least one inorganic material covering at least a portion of at leastone surface of a fullerene and methods for making. The present inventionfurther relates to composites comprising the coated fullerenes of thepresent invention and further comprising polymers, ceramics and/orinorganic oxides. A coated fullerene interconnect device wherein atleast two fullerenes are contacting each other to form a spontaneousinterconnect is also disclosed as well as methods of making. Inaddition, dielectric films comprising the coated fullerenes of thepresent invention and methods of making are further disclosed.

BACKGROUND OF THE INVENTION

Fullerenes are broadly defined as the third form of the element carbonafter diamond and graphite. Fullerenes are molecular solids that consistof fused six-membered and five-membered rings. Two general types offullerenes may be described: Buckyballs and carbon nanotubes. Buckyballshave spherical structures and are typified by C₆₀. Other sphericalfullerenes include C₇₀ and higher oligomers. Single walled carbonnanotubes (SWNTs) are elongated members of the fullerene family.

The interior cavity of a fullerene can accommodate an atom, molecule, orparticle, depending on the volume circumscribed by the structure of thefullerene, to provide so-called doped fullerenes. Furthermore,fullerenes may be chemically functionalized by reacting the surfaceunder suitable conditions to form either covalent, van der Waals ordipolar interactions with a chemical substituent.

SWNTs have come under intense multidisciplinary study because of theirunique physical and chemical properties and their possible applications.The electronic characteristics of SWNT can be described as metallic orsemiconducting; such characteristics deriving from the helicity anddiameter of the SWNT. More importantly, it has been shown that theseelectronic properties are sensitive to the environment surrounding theSWNT. For example, it is well known that the presence of certainmolecules, such as O₂ or NH₃, may alter the overall conductivity ofSWNTs through the donation or acceptance of electrons. Such propertiesmake SWNT ideal for nanoscale sensing materials. Nanotube field effecttransistors (FETs), for example, have already been demonstrated as gassensors. It is thought that selectivity in nanotube sensors can beachieved through the placement of specific functional groups on thenanotube surface; such groups having the requisite ability toselectively bind specific target molecules. Working against this goal isthe fact that functionalization changes the electronic properties fromthat of a semiconductor or conductor to that of an insulator. Moreover,chemical functionalization of SWNT is not as of yet regiospecific. Afurther major obstacle to such efforts has been diversity of tubediameters, chiral angles, and aggregation states of the tubes.Aggregation is particularly problematic because highly polarizable,smooth sided SWNTs readily form bundles or ropes with van der Waalsbinding energy of ca. 500 eV per micrometer of tube contact. Thisbundling perturbs the electronic structure of the tubes and precludesthe separation of SWNTs by size or type.

SWNT-based composites can provide excellent electronic and/or mechanicalproperties upon incorporation into a suitable matrix. Carbon nanotubesare excellent candidates for the fabrication of robust composites, andconducting polymers, due to their fascinating electronic and mechanicalproperties. Unfortunately, two issues must be overcome prior todevelopment of large-scale applications. First, the SWNTs must be stablewithin a desired matrix. Second, the aggregation of SWNTs into ropes andbundles requires high loading that is uneconomic and represents a wasteof materials.

The first of these issues requires that the SWNTs be protected fromsubsequent processing, e.g., oxidation. In addition, the formation of astable tube/matrix interface is critical for composite applications.Surface treatments are required to ensure efficient tube-matrixinteractions. Unfortunately, these treatments can result in thedegradation of the tubes. The second of these issues requires thatindividual SWNTs (rather than bundles) be employed to maximize theimpact of the SWNTs at the lowest possible loading.

It has been shown that individual SWNTs may be obtained encased in acylindrical micelle, by ultrasonically agitating an aqueous dispersionof raw SWNTs in the presence of a suitable surfactant (O'Connell et al.,2002). Upon drying the micellular solution, however, bundles re-form.SWNTs have been encased in a wide range of organic materials. It wouldbe desirable to fabricate individually coated SWNTs where the coating isretained in solution and the solid state. Of particular interest aredielectric materials such as silica, which may also be compatible withcomposite matrix materials. Silica is an example of an inorganic oxide.

Coating of SiO₂ on multiwalled carbon nanotubes (MWNTs) has beenreported (Seeger et al., 2001). However, these coatings required asol-gel type of reaction and extremely long reaction times on the orderof 150 hours. Coatings have also been reported on SWNTs, but theserequire isolation of the tubes on a surface prior to reaction. It wouldbe advantageous if there was a method by which individual fullerenes andindividual SWNT could be coated under near ambient temperatures withreaction times on the order of a few hours, without the need forisolation on a surface prior to coating.

The classical sol-gel process for generating thin films of an oxide,such as silica, on substrates can be divided into three steps. First,preparation of a stable dispersion of colloidal oxide particles in aliquid, “sol formation”. Second, aggregation of the particles toencompass the liquid, “gel formation”, and deposition of the resultinggel on the surface of the substrate. Third, removal of the solvent bydrying and/or heating (Vossen, et al., 2000).

In contrast, the liquid phase deposition, “LPD”, of silica fromsaturated fluorosilicic acid solutions involves the reaction of waterwith silica precursors that are solvated at the molecular level togenerate silica gels that deposit onto the surface of the substrate(Yeh, et al., 1994). Whereas film growth in the sol-gel method islargely dependent on the size of the initial colloidal particles and itsinfluence on their aggregation, growth in the LPD method is morecontrolled since it continues layer by layer as more molecules react onthe surface of the substrate. The important step in LPD is to provide anactive site for growth to occur on a surface.

The semiconductor industry has targeted the development of theinterlayer and intrametal dielectric for the next several generations ofhigher density, faster computer chips, as specified by the milestonesset out in the International Technology Roadmap for Semiconductors (theITRS.) There is still no acceptable material or process that producesfilms with the desired values of low dielectric constant (k value)concurrently with optimum electro- and thermo-mechanical properties.Current processes are based either on sol-gel methods for filmdeposition and growth, or on low temperature chemical vapor deposition(CVD) of carbon or fluorine-containing silicon dioxide films. The kvalues achieved by these processes are in the range from ˜2.7 to greaterthan 3, still well above the maximum value of 2 required by the industryin order to meet the chip performance milestones identified in the ITRS.

Silicon dioxide (SiO₂) forms the basis of planar silicon chiptechnology. Insulator coatings for electronic and photonic deviceslayers are most frequently formed by thermal oxidation of silicon (Si)in the temperature range 900 to 1200° C. SiO₂ is also deposited bychemical vapor deposition (CVD) techniques at lower temperatures (200 to900° C.) on various substrates. The growth of insulator films at lowtemperatures is very attractive for most device applications due toreduced capital cost, high output and freedom from technologicalconstraints associated with the growth of dielectric thin films usingconventional high-temperature growth/deposition techniques. Depositionof SiO₂ insulator layers from solution is previously known usingorgano-metallic solutions. In this procedure, the insulator layer isapplied onto the substrate either by dipping the substrate into thesolution or by spinning the substrate after a small amount of thesolution is applied onto the surface. In both cases the substrate isthen placed in an oven to drive off the solvent.

Attempts to produce porous silicon dioxide have failed to produce filmswith isolated voids and uniform void size, resulting in poor processreproducibility and film quality. Such processes also require the use ofheat to evaporate a solvent or other component from the film to createthe voids, something not required by the present invention.

CVD (chemical vapor deposition) requires the pyrolysis or photolysis ofvolatile compounds to create chemical fragments that are deposited onthe surface of a substrate. The temperature of substrate is sufficientlyhigh to allow mobility of fragments on the growth surface. Thesefragments travel around the surface until they find thermodynamicallystable sites to which they attach. In this way the quality of CVD filmsis usually high. Thus, CVD uses surface growth. If gas phase growthoccurs, uniform films are not produced. Instead, nanoparticles can form,from which films form after agglomeration. The resulting film requiresfurther thermal processing in order to become uniform. Disadvantageswith CVD include the high temperatures required and the use of volatilecompounds or low pressures. Each of these adds to the environmental loadof the process. Sol-gel is low temperature method. Precursor compoundsare dissolved in solution and reacted with additional reagents (usuallywater or an acid) to give a gel. If a film or coating is required, thenthe gel must be spin-coated onto the substrate. Since most sol-gelsconsist of nanoparticles or clusters with a significant organic content,additional thermal or chemical treatments are required to form a trueinorganic material.

SUMMARY OF THE INVENTION

The present invention discloses, in one aspect, a method of making acoated fullerene comprising a layer of at least one inorganic materialcovering at least a portion of at least one surface of a fullerenewherein the method comprises (a) dispersing a fullerene under suitableconditions to provide a dispersed fullerene; and (b) depositing at leastone inorganic material under suitable conditions onto at least onesurface of the dispersed fullerene.

In another aspect, the present invention discloses a coated fullerenecomprising a layer of at least one inorganic material covering at leasta portion of at least one surface of a fullerene. The coated fullereneof the present invention is substantially similar to the coatedfullerene described in connection with a previous aspect of thisinvention.

In yet another aspect of the present invention is disclosed, a compositecomprising a coated fullerene comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof a fullerene; and at least one composite matrix selected from thegroup consisting of polymers, ceramics and inorganic oxides.

In still another aspect is presented a method of making a coatedfullerene interconnect device comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof fullerenes wherein at least two fullerenes are contacting each otherto form a spontaneous interconnect; and at least one suitable metalcontact is found at the site of at least one spontaneous interconnectwherein said method comprises (a) dispersing a fullerene under suitableconditions to provide a dispersed fullerene; (b) depositing at least oneinorganic material under suitable conditions onto at least one surfaceof the dispersed fullerene to provide a coated fullerene; (c) isolatingthe coated fullerene; (d) removing at least a portion of the layer ofinorganic material in a manner suitable for permitting at least twofullerenes to contact each other to provide at least one spontaneousinterconnect; (e) optionally, separating at least one spontaneousinterconnect; (f) optionally, allowing at least two fullerenes tocontact each other to provide at least one new spontaneous interconnect;and (g) depositing a suitable metal contact at the site of at least onespontaneous interconnect and/or one new spontaneous interconnect.

In another aspect of the present invention is disclosed a coatedfullerene interconnect device comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof fullerenes wherein at least two fullerenes are contacting each otherto form a spontaneous interconnect; and at least one suitable metalcontact is found at the site of at least one spontaneous interconnect.

In one more aspect, the present invention provides dielectric filmscomprising the coated fullerenes of the present invention. Thedielectric films of the present invention are particularly well suitedfor use as interlayer or intermetal dielectric on silicon-based computerchips.

Possible applications for this invention include, but are not limitedto, the following:

(1) Growth of insulating layers for nano-based chips. A new generationof nanotube or nanowire chips is being developed. At present these are2D devices, however, in order for vertical integration to be developed atechnology of low temperature insulator growth is required. A low kdielectric is not a requirement at present; oxide and silica films aretherefore of potential interest for early generation devices.

(2) Growth of low k dielectric layers for advanced semiconductor chipfabrication. Insulating oxides (especially silica) are used asinsulation layers in present chip technology. These are presentlyprepared by thermal oxidation, CVD, and sol gel techniques and have onlylimited success in achieving low k dielectric films. Additionally, aroom temperature, or near room temperature, solution process would becost effective.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiments of thepresent invention, reference will be made to the accompanying drawings,wherein:

FIG. 1: SEM image, at 15,000×, of silica product without particlesadded.

FIG. 2: SEM image, at 15,000×, of product of LPD silica reaction withfullerene added to reaction mixture.

FIG. 3: SEM image, at 15,000×, of product of LPD silica reaction withfullerenol added to reaction mixture.

FIG. 4: SEM image, at 50,000×, of product of LPD silica reaction withfullerenol added to reaction mixture.

FIG. 5: SEM image, at 50,000×, of product of LPD silica reaction withfullerenol added to reaction mixture.

FIG. 6: SEM image, at 5,000×, of product of LPD silica reaction withfullerenol added to reaction mixture.

FIG. 7: SEM image, at 100,000×, of product of LPD silica reaction withfullerenol added to reaction mixture.

FIG. 8: SEM image, at 6500×, of a silicon chip coated with silica-coatedfullerenols.

FIG. 9: SEM image, at 35,000×, of a silicon chip coated withsilica-coated fullerenols.

FIG. 10: SEM image, at 15,000×, of twice-coated silicon chip.

FIG. 11: SEM image, at 35,000×, of twice-coated silicon chip.

FIG. 12: SEM image, at 50×, of glass slide coated with silica coatedfullerenols.

FIG. 13: SEM image, at 15,000×, of the product of the reaction of SDSwith the LPD silica solution.

FIG. 14: SEM image, at 50,000×, of the product of the reaction of SDSwith the LPD silica solution.

FIG. 15: SEM image, at 15,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 16: SEM image, at 120,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 17: SEM image, at 25,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 18: SEM image, at 120,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 19: SEM image, at 20,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 20: SEM image, at 150,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 21: SEM image, at 25,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 22: SEM image, at 200,000×, of the product of the reaction of SDSdispersed SWNTs with the LPD silica solution.

FIG. 23: SEM image, at 50,000×, of selectively etched silica coatedSWNT.

FIG. 24: SEM image, at 25,000×, of selectively etched silica coatedSWNT.

FIG. 25: SEM image, at 20,000×, of the product of the reaction of DTABdispersed SWNTs with the LPD silica solution.

FIG. 26: SEM image, at 12,000×, of the product of the reaction of DTABdispersed SWNTs with the LPD silica solution.

FIG. 27: TEM image, at 200,000×, of the product of the reaction of DTABdispersed SWNTs with the LPD silica solution.

FIG. 28: SEM image, at 65,000×, of the product of the reaction of DTABdispersed SWNTs with the LPD silica solution.

FIG. 29: Thin silica-SWNT paper formed by light etching of coatednanotubes.

DETAILED DESCRIPTION OF THE INVENTION

This invention discloses the use of liquid phase deposition to preparecoated fullerenes. Such coated fullerenes may be spherical, such as C₆₀,or single walled nanotubes (SWNT). The present invention appliesspecifically to coating fullerenes with an inorganic material, such as,for example, an inorganic oxide typified by silica. The presentinvention also discloses a method for growing films of inorganic oxidescomprising fullerenes in a mariner suitable for providing porousinorganic oxide films possessing desirable electronic and mechanicalproperties.

Method of Making a Coated Fullerene

The present invention discloses, in one aspect, a method of making acoated fullerene comprising a layer of at least one inorganic materialcovering at least a portion of at least one surface of a fullerenewherein the method comprises (a) dispersing a fullerene under suitableconditions to provide a dispersed fullerene; and (b) depositing at leastone inorganic material under suitable conditions onto at least onesurface of the dispersed fullerene.

As used herein, fullerene is any carbonaceous material wherein thestructure is a regular, three dimensional network of fused carbon ringsarranged in any one of a number of possible structures including, butnot limited to, cylindrical, spherical, ovoid, oblate or oblong. Commonfullerenes include the cylindrical carbon nanotube and the icosahedralC₆₀ carbon molecules. In particular, the fullerene is preferablyselected from the group consisting of C₆₀, C₇₂, C₈₄, C₉₆, C₁₀₈, C₁₂₀,single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes(MWNT). In one preferred embodiment of the process, the fullerene isC₆₀. In another preferred embodiment of the process, the fullerene is asingle walled carbon nanotube (SWNT). Single-walled carbon nanotubesdiffer from multi-walled carbon nanotubes based on the number ofconcentric tubes present; single-walled carbon nanotubes comprise onlyone tube about a given center whereas multi-walled carbon nanotubes haveat least two, and often more, nested tubes about a common center.

All carbon nanotubes tend to agglomerate into ropes and bundles of manycarbon nanotubes and it is ordinarily quite difficult to obtainindividual, dispersed carbon nanotubes. In one embodiment of the presentprocess using single-walled carbon nanotubes (SWNT), either aggregatedor individually dispersed tubes may be used. Special techniques areusually required to obtain individually dispersed carbon nanotubes andthe methods used in the present invention will be discussed hereinbelow.In a particularly preferred embodiment of the present process, thefullerene is an individual single-walled carbon nanotube (SWNT).

The coated fullerene of the present method comprises a layer of at leastone inorganic material. As defined here, an inorganic oxide will be anymaterial comprising at least one inorganic element and oxygen; the oxidemay additionally comprise other elements including, but not limited to,for example, hydrogen and fluorine. Although any one of a number ofinorganic materials may be suitable for use in the present method, apreferred inorganic material is an inorganic oxide. In particular,although any one of a number of inorganic oxides could suffice in thepresent method, a preferred oxide is the oxide of silicon. Therefractive index of the silica coatings used so far may be alteredwithin a modest range.

The present method comprises dispersing a fullerene under suitableconditions to provide a dispersed fullerene. Though not wishing to bebound by any particular theory, it is believed that the process ofdispersing a fullerene serves the dual purpose of allowing the fullereneto be soluble thereby permitting for the deposition of an inorganicmaterial around individual tubes; and activating the tubes fordeposition of an inorganic material. Suitable conditions for dispersinga fullerene comprise the use of a suitable solvent; water is aparticularly preferred solvent. Suitable conditions may further comprisea particular technique to disperse fullerenes. Preferred techniquesinclude chemical functionalization and surfactant addition.

Though not wishing to be bound by any particular theory, it is believedthat chemical functionalization provides at least one, and possiblyseveral, specific reactive site(s) that act as sites that initiategrowth of the layer of inorganic material. In one embodiment, thefullerene is dispersed by a technique of chemical functionalization. Asused herein, chemical functionalization is any chemical reaction thatmodifies and/or adds chemical groups to the surface of fullerene toleave a reactive group at a surface of a fullerene. Although there aremany different chemical reactions that could be useful in the chemicalfunctionalization of the present invention, it has been discovered thathydroxylation is a particularly useful chemical reaction for thechemical functionalization of the present invention.

The presence of surface hydroxylate groups on at least a portion of onesurface of a fullerene tends to impart greater solubility to thefullerene in water, thereby discouraging aggregation. The hydroxylationallows for the fullerenes to be dispersed in aqueous solution therebyfacilitating possible subsequent deposition.

In an alternate embodiment, the fullerene is dispersed by a technique ofsurfactant addition. Without wishing to be bound by any particulartheory, it is believed that the surfactant surrounds the fullerenes andprovides the required solubility while also assisting in dispersion ofindividual fullerenes. In one preferred embodiment, a single-walledcarbon nanotube is dispersed by surfactant addition. According to thisembodiment, the technique of surfactant addition may comprise theaddition of sodium dodecylsulfate and/or dodecyltrimethyl ammoniumbromide. The ability to uniformally coat individual SWNTs rather thanropes and bundles is a consequence of using a surfactant that is notaffected by pH.

The present method still further comprises depositing at least oneinorganic material under suitable conditions onto at least a portion ofone surface of the dispersed fullerene. In one preferred embodiment,depositing at least one inorganic material under suitable conditionscomprises contacting the dispersed fullerene with a solution comprisingsilica. According to this embodiment, the silica is preferably at leastpartially dissolved in the solution; and more preferably the solutionfurther comprises H₂SiF₆. It is also important to employ a non sol-gelapproach to allow seeded growth on the surface of the SWNT.

According to this embodiment, but without wishing to be bound by anyparticular theory, it is believed that fluorosilicic acid can react withbase to produce silica, as shown in Equation (1).

H₂SiF₆+2OH⁻

SiO₂+2F⁻+4HF  (1)

Chemically functionalized substrates, such as hydroxylated C₆₀, canreact with the acid in a condensation reaction, in turn acting as anucleation site to begin layer growth as shown in Equation (2).

12H₂SiF₆+C₆₀(OH)₂₄ ^(n−)

C₆₀(SiO₂)₁₂+24F⁻+48HF  (2)

Growth occurs at the initial silicate and reacts with additionalfluorosilicic acid to grow layers of silica on the particle.

A key advantage of the present invention is that the rate of formationof deposition is significantly faster than that reported in the priorart. In addition, coating individual single-walled carbon nanotubes(SWNT) by a solution process has not been possible until now. Accordingto the present method, depositing at least one inorganic materialpreferably takes place at a rate no less than 10 nm/hour.

The present method may further comprise isolating the coated fullerene.This is most preferably done using any technique of centrifugation.After the coating has reached the desired thickness, the coatingreaction is quenched and the coated fullerenes may be isolated bycentrifuge. The supernatant liquid is disposed of and the solid isre-dispersed in a suitable solvent such as ethanol. Thiscentrifugation/re-dispersion process is repeated as required to purifythe coated fullerenes. The coated SWNTs are then characterized inethanol suspension or as a dried powder.

A Coated Fullerene

In another aspect, the present invention discloses a coated fullerenecomprising a layer of at least one inorganic material covering at leasta portion of at least one surface of a fullerene. The coated fullereneof the present invention is substantially similar to the coatedfullerene described in connection with a previous aspect of thisinvention.

The coated fullerene comprises at least one inorganic material.Preferably, at least one inorganic material is an inorganic oxide; morepreferably, an inorganic oxide is silica. The fullerene comprising thecoated fullerene is preferably selected from the group consisting ofC₆₀, C₇₂, C₈₄, C₉₆, C₁₀₈, C₁₂₀, single-walled carbon nanotubes (SWNT),and multi-walled carbon nanotubes (MWNT). The coated fullerene maycomprise a fullerene doped with at least one type of metal. As usedherein, a doped fullerene will be a fullerene comprising at least onemetal wherein the atoms of metal may be within, adsorbed on, orincorporated into the fullerene. The coated fullerene may comprise afullerene that is a single walled carbon nanotube (SWNT). The singlewalled carbon nanotubes (SWNT) may be present in the form of ropes,bundles, or individual tubes. In a preferred embodiment, thesingle-walled carbon nanotubes (SWNT) are present in the form ofindividual tubes. According to this embodiment, the coated fullerenefurther comprises at least one inorganic material. Preferably, this isan inorganic oxide; more preferably, silica. Also according to thisembodiment, the coated fullerenes may be handled as a solid without anysubstantial change in physical, electrical or mechanical properties. Thecoated fullerenes of the preferred embodiment will also showcharacteristic bands in the Raman spectrum indicative of individualtubes. In addition, the coated fullerenes show no change in fluorescenceintensity until the thickness of the coating is sufficient to causescattering of the emitted light. This indicates that the coating doesnot alter the electrical properties and therefore the band gap of thefullerenes.

The prior art has shown that individual SWNTs strongly fluoresce insolution in the presence of a surfactant; in particular, excitation at532 nm results in an emission between 950-1400 nm. This fluorescence isquenched under conditions that permit for the aggregation of SWNT intoropes and bundles, namely pH<5. The silica-coated single-walled carbonnanotubes of the present invention fluoresce in solution suggesting thatindividual single-walled carbon nanotubes rather than ropes have beensuccessfully coated.

Composites

In yet another aspect of the present invention is disclosed, a compositecomprising a coated fullerene comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof a fullerene; and at least one composite matrix selected from thegroup consisting of polymers, ceramics and inorganic oxides.

The fullerenes used in the current aspect may be selected from the groupconsisting of C₆₀, C₇₂, C₈₄, C₉₆, C₁₀₈, C₁₂₀, single-walled carbonnanotubes (SWNT) and multi-walled carbon nano-tubes (MWNT). Thefullerenes are more preferably C₆₀ or single-walled carbon nanotubes;but is most preferably single-walled carbon nanotubes (SWNT). In onepreferred embodiment, at least a portion of at least one surface of afullerene is chemically functionalized. In another preferred embodiment,at least one inorganic material is preferably an inorganic oxide; butmost preferably, an inorganic oxide is silica.

Method of Making a Coated Fullerene Interconnect Device

The creation of device structures using fullerenes in an assembled arrayto create a specific device is of considerable interest. The creation oftwo- and three-dimensional structures comprising coated fullerenes andspontaneous interconnects' led us to fabricate multi-function devices.Spontaneous interconnects will be defined as points of contact betweenat least two fullerenes. Gold connections may be deposited at the sitesof these spontaneous interconnects to preferably provide devicescomprising numerous connections between individual fullerenes.

In still another aspect is presented a method of making a coatedfullerene interconnect device comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof fullerenes wherein at least two fullerenes are contacting each otherto form a spontaneous interconnect; and at least one suitable metalcontact is found at the site of at least one spontaneous interconnectwherein said method comprises (a) dispersing a fullerene under suitableconditions to provide a dispersed fullerene; (b) depositing at least oneinorganic material under suitable conditions onto at least one surfaceof the dispersed fullerene to provide a coated fullerene; (c) isolatingthe coated fullerene; (d) removing at least a portion of the layer ofinorganic material in a manner suitable for permitting at least twofullerenes to contact each other to provide at least one spontaneousinterconnect; (e) optionally, separating at least one spontaneousinterconnect; (f) optionally, allowing at least two fullerenes tocontact each other to provide at least one new spontaneous interconnect;and (g) depositing a suitable metal contact at the site of at least onespontaneous interconnect and/or one new spontaneous interconnect.

According to the present aspect, fullerenes are selected from the groupconsisting of C₆₀, C₇₂, C₈₄, C₉₆, C₁₀₈, C₁₂₀, single-walled nanotubes(SWNT) and multi-walled nanotubes (MWNT). Preferably, the fullerenes aresingle-walled carbon nanotubes (SWNT).

The present coated fullerene interconnect device comprises a layer of atleast one inorganic material. Preferably, at least one inorganicmaterial comprises an inorganic oxide; more preferably, an inorganicoxide is an oxide of silicon.

The present method of making a coated fullerene interconnect devicecomprises dispersing a fullerene under suitable conditions to provide adispersed fullerene. Preferably, the fullerene is dispersed by atechnique of chemical functionalization or surfactant addition.

The present method further comprises removing at least a portion of thelayer of inorganic material; preferably this comprises treatment with asuitable etchant. In one embodiment, removing at least a portion of thelayer of inorganic material is effective in removing all of theinorganic material. In another embodiment, at least a portion of thelayer of inorganic material comprises selectively removing inorganicmaterial from the ends of the fullerenes. In yet another embodiment,removing at least a portion of the layer of inorganic material in asuitable manner comprises selectively removing inorganic material fromthe central portion of the fullerenes.

The present method may further comprise allowing at least two fullerenesof at least one spontaneous contact to separate; this preferablycomprises treatment with a suitable surfactant. The present methodfurther comprises, optionally, allowing at least two fullerenes tocontact each other to provide at least one new spontaneous interconnect.

According to a preferred embodiment, the number and nature of newspontaneous interconnects will differ from that observed for the firstspontaneous interconnect. According to this embodiment, steps (e) and(f) may be repeated until a desired profile of electroniccharacteristics has been attained. Preferably, the characteristics maybe those found in electronic switching and memory devices.

According to a preferred embodiment, the present method furthercomprises testing the coated fullerene interconnect devices forsuitability as electronic devices.

A Coated Fullerene Interconnect Device

In another aspect of the present invention is disclosed a coatedfullerene interconnect device comprising a layer of at least oneinorganic material covering at least a portion of at least one surfaceof fullerenes wherein at least two fullerenes are contacting each otherto form a spontaneous interconnect; and at least one suitable metalcontact is found at the site of at least one spontaneous interconnect.

Preferably, the present coated fullerene interconnect device performssome electronic switching or memory function.

Dielectric Films Comprising Coated Fullerenes

One embodiment of the present invention is to dispense the previouslycoated fullerenes into the interlayer dielectric (ILD) or intermetaldielectric (IMD) layer growth process in such a manner as to achieve aspecific void volume in the layer, while retaining the mechanical andelectrical properties of the layer required for successful chipfabrication and performance. This invention provides a way to combinethe above approaches to give a low temperature solution process thatallows for the formation of uniform films; the films can be preparedwith a variety of properties optimized for specific applications.

The second is to grow multiple layers of the porous oxide films on largearea wafers at the appropriate process steps in chip fabrication. Thefirst layer of porous silicon dioxide with fullerene inclusions must begrown directly on the silicon wafer after it has been patterned withnano-scale transistors, and may use a different solution from that usedto coat the fullerenes. All subsequent porous films must be grown oncomposite surfaces consisting of sub-micron width copper lines embeddedin previously grown porous SiO₂ films, and may use yet another solutioncompared to those mentioned above.

Prior art attempts to produce porous silicon dioxide have failed toproduce films with isolated voids and uniform void size, resulting inpoor process reproducibility and film quality. Such processes alsorequire the use of heat to evaporate a solvent or other component fromthe film to create the voids, something not required by the presentinvention. The present process will produce distinct voids ofcontrollable size in a film with superior properties compared to the CVDand sol gel processes with which it competes.

EXAMPLES

The following examples are presented to illustrate the ease andversatility of the approach and are not to be construed as the onlyexamples of the proposed approach or as limiting the scope of thepresent invention. It is understood that a practitioner, of ordinaryskill in the art, will be able to employ alternative reagents andcoatings to achieve similar results.

Example 1

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M withMillipore (UP) water. A sample of this solution (10 mL) was allowed toreact in a plastic centrifuge tube. This mixture was stirred, at 30° C.,for 3 hours. The product was then filtered, washed with UP water, driedand analyzed as a powder.

Example 2

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (10 mL) was allowed to react withfullerene (10 mg) in a plastic centrifuge tube. This mixture wasstirred, at 30° C., for 3 hours. The product was then filtered, washedwith UP water, dried and analyzed as a powder.

Example 3

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (10 mL) was allowed to react withfullerenol (10 mg) in a plastic centrifuge tube. This mixture wasstirred, at 30° C., for 12 hours. The product was then filtered, washedwith UP water, dried and analyzed as a powder.

Example 4

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (5 mL) was allowed to react withfullerenol (5 mL of a 50 mg/L solution) in a plastic centrifuge tube.This mixture was stirred, at 30° C., for 12 hours. The product was thencentrifuged at 4000 rpm for 60 minutes. The supernatant liquid wasdiscarded. The product was then redispersed in ethanol by sonification.This process was repeated six times. The product was then dried andanalyzed as a powder.

Example 5

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (20 mL) was allowed to react withfullerenol (10 mg) in a plastic centrifuge tube. This mixture wasstirred, at 30° C., for 3 hours. The product was then centrifuged at4000 rpm for 60 minutes. The supernatant liquid was discarded. Theproduct was then redispersed in ethanol by sonification. This processwas repeated six times. The product was then dried and analyzed as apowder.

Example 6

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was diluted to 1.00 M. Fullerenols(10 mg) were added to a sample of this solution (50 mL) and allowed toreact in a Tupperware container. To this mixture was added a siliconchip which had been etched first in RCA-1 etch (NH₄OH:H₂O₂:H₂O),followed by a Millipore water rinse and then etched with an RCA-2 etch(HCl:H₂O₂:H₂O) and again rinsed. The solution with the chip was stirred,at 30° C., for 4 hours. The chip was then removed from the solution,rinsed in Millipore water and dried with compressed air.

Example 7

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was diluted to 1.00 M. Fullerenols(10 mg) were added to a sample of this solution (50 mL) and allowed toreact in a Tupperware container. To this mixture was added a siliconchip which had been previously coated with silica-coated fullerenols.The solution with the chip was stirred, at 30° C., for 4 hours. The chipwas then removed from the solution, rinsed in Millipore water and driedwith compressed air.

Example 8

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (50 mL) was allowed to react withfullerenol (10 mg) in a plastic centrifuge tube. This mixture wasstirred, at 30° C., for 3 hours. The product was then centrifuged at4000 rpm for 60 minutes. The supernatant liquid was discarded. Theproduct was then redispersed in ethanol by sonification. This processwas repeated six times. The product, dispersed in ethanol, wastransferred to a clean scintillation vial. A glass slide, which had beencleaned in a base bath, copiously rinsed in UP water and stored inethanol, was placed upright in the scintillation vial. The solution wasthen allowed to evaporate overnight. The coated fullerenols coated theglass slide via capillary action.

Example 9

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The solution was then diluted to 1.0 M with UPwater. A sample of this solution (100 mL) was allowed to react withsodium dodecylsulfate (SDS, 1 mL of a 1% solution) in a plasticcentrifuge tube. This mixture was stirred, at 30° C., for 3 hours. Theproduct was then centrifuged at 4000 rpm for 60 minutes. The supernatantliquid was discarded. The product was then redispersed in ethanol bysonification. This process was repeated six times. The product was thendried and analyzed as a powder.

Example 10

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (100 mL) was added to a1% SDS solution(1 mL) containing dispersed single walled carbon nanotubes (SWNT, 50mg/L). These were allowed to react in a plastic centrifuge tube, withstirring, at 30° C., for four hours. The reaction was then quenched withethanol and centrifuged at 4400 rpm for 15 minutes. The supernatantliquid was disposed of and the solid was redispersed in ethanol. Thisprocess was repeated six times. The coated SWNTs were then characterizedin ethanol solution or as a dried powder.

Example 11

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (5 mL) was added to a1% SDS solution(5 mL) containing dispersed SWNT (50 mg/L). These were allowed to reactin a plastic centrifuge tube, with stirring, at 30° C., for four hours.The reaction was then quenched with ethanol and centrifuged at 4400 rpmfor 15 minutes. The supernatant liquid was disposed of and the solid wasredispersed in ethanol. This process was repeated six times. The coatedSWNTs were then characterized in ethanol solution or as a dried powder.

Example 12

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (3 mL) was added to a1% SDS solution(6.25 mL) containing dispersed SWNT (40 mg/L). These were allowed toreact in a plastic centrifuge tube, with stirring, at 30° C., for fourhours. The reaction was then quenched with ethanol and centrifuged at4400 rpm for 15 minutes. The supernatant liquid was disposed of and thesolid was redispersed in ethanol. This process was repeated six times.The coated SWNTs were then characterized in ethanol solution or as adried powder.

Example 13

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (1 mL) was added to a1% SDS solution(6.25 mL) containing dispersed SWNT (40 mg/L). These were allowed toreact in a plastic centrifuge tube, with stirring, at 30° C., for fourhours. The reaction was then quenched with ethanol and centrifuged at4400 rpm for 15 minutes. The supernatant liquid was disposed of and thesolid was redispersed in ethanol. This process was repeated six times.The coated SWNTs were then characterized in ethanol solution or as adried powder.

Example 14

Products from Examples 12 and 13 were dried on a surface and selectivelyetched with hydrofluoric acid (1%). They were then thoroughly rinsedwith UP water and dried for characterization.

Example 15

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (1 mL) was added to a1%dodecyltrimethyl ammonium bromide solution (DTAB, 5 mL) containingdispersed SWNT (30 mg/L). These were allowed to react in a plasticcentrifuge tube, with stirring, at 30° C., for twelve hours. Thereaction was then quenched with ethanol and centrifuged at 4400 rpm for15 minutes. The supernatant liquid was disposed of and the solid wasredispersed in ethanol. This process was repeated six times. The coatedSWNTs were then characterized in ethanol solution or as a dried powder.

Example 16

Fumed silica (3.0 g) was added to 50 mL of 3.20 M fluorosilicic acidsolution (H₂SiF₆: Riedel de Haen, 34% pure) and allowed to stirovernight. This solution was then filtered, by vacuum, through a 0.22micron Millipore filter. The filtrate was diluted to 1.0 M with UPwater. A portion of this solution (1 mL) was added to a1% DTAB solution(8.33 mL) containing dispersed SWNT (30 mg/L). These were allowed toreact in a plastic centrifuge tube, with stirring, at 30° C., forfifteen minutes. The reaction was then quenched with ethanol andcentrifuged at 4400 rpm for 15 minutes. The supernatant liquid wasdisposed of and the solid was dispersed in ethanol. This process wasrepeated six times. The coated SWNTs were then characterized in ethanolsolution or as a dried powder.

Example 17

A sample of the product from example 16 was dried on a surface and thenquickly etched with hydrofluoric acid. After a defined time period, theetch was quenched in UP water. The etched material was then allowed todry on a metal stub. A thin coated SWNT paper was formed.

Example 18

A sample of the product of example 16, dispersed in ethanol was added topowdered PVP, with stirring. Once the solvent had evaporated, a sampleof polymer with well-dispersed coated nanotubes was obtained.

1. A coated fullerene comprising a layer of at least one inorganicmaterial covering at least a portion of at least one surface of afullerene.
 2. The coated fullerene according to claim 1, wherein the atleast one inorganic material is an inorganic oxide.
 3. The coatedfullerene according to claim 2, wherein the inorganic oxide is silica.4. The coated fullerene according to claim 1, wherein the fullerene isselected from the group consisting of C₆₀, C₇₂, C₈₄, C₉₆, C₁₀₈, C₁₂₀,single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes(MWNT), and combinations thereof.
 5. The coated fullerene according toclaim 4, wherein the at least one inorganic material is an inorganicoxide.
 6. The coated fullerene according to claim 5, wherein theinorganic oxide is silica.
 7. The coated fullerene according to claim 4,wherein the fullerene is doped with at least one type of metal.
 8. Thecoated fullerene according to claim 7, wherein the at least oneinorganic material is an inorganic oxide.
 9. The coated fullereneaccording to claim 8, wherein the inorganic oxide is silica.
 10. Thecoated fullerene according to claim 4, wherein the fullerene is a singlewalled carbon nanotube (SWNT).
 11. The coated fullerene according toclaim 10, wherein the SWNT is present in the form of ropes, bundles, orindividual tubes.
 12. The coated fullerene according to claim 11,wherein the SWNT is present in the form of individual tubes.
 13. Thecoated fullerene according to claim 12, wherein the at least oneinorganic material is an inorganic oxide.
 14. The coated fullereneaccording to claim 13, wherein the inorganic oxide is silica.
 15. Thecoated fullerene according to claim 14, wherein the fullerenes ishandled in the solid state without undergoing any substantial change inelectrical or mechanical properties.
 16. The coated fullerene accordingto claim 14, wherein the coated fullerenes show bands in the Ramanspectrum characteristic of individual fullerenes.
 17. The coatedfullerene according to claim 16, wherein the coated fullerenes show nochange in fluorescence until the thickness of the coating is sufficientto cause light scattering.
 18. The coated fullerene according to claim1, wherein the coated fullerene is used in the interlayer dielectric(ILD) or intermetal dielectric (IMD) of a silicon transistor chip.
 19. Acomposite comprising a coated fullerene comprising: a layer of at leastone inorganic material covering at least a portion of at least onesurface of a fullerene; and at least one composite matrix selected fromthe group consisting of polymers, ceramics, inorganic oxides, andcombinations thereof.
 20. The composite according to claim 19, whereinthe fullerene is selected from the group consisting of C₆₀, C₇₂, C₈₄,C₉₆, C₁₀₈, C₁₂₀, single-walled carbon nanotubes (SWNT), multi-walledcarbon nanotubes (MWNT), and combinations thereof.
 21. The compositeaccording to claim 20, wherein the fullerene is C₆₀ or single-walledcarbon nanotubes (SWNT).
 22. The composite according to claim 20,wherein the fullerene is single-walled carbon nanotubes (SWNT).
 23. Thecomposite of claim 20, wherein the at least a portion of the at leastone surface of a fullerene is chemically functionalized.
 24. Thecomposite of claim 19, wherein the at least one inorganic material is aninorganic oxide.
 25. The composite of claim 24, wherein the inorganicoxide is silica.
 26. The composite of claim 25, wherein the composite isused in a thin film.
 27. A method of making a coated fullereneinterconnect device comprising a layer of at least one inorganicmaterial covering at least a portion of at least one surface offullerenes wherein: at least two fullerenes are contacting each other toform a spontaneous interconnect; and at least one suitable metal contactis found at the site of at least one spontaneous interconnect, whereinsaid method comprises: (a) dispersing a fullerene under suitableconditions to provide a dispersed fullerene; (b) depositing at least oneinorganic material under suitable conditions onto at least one surfaceof the dispersed fullerene to provide a coated fullerene; (c) isolatingthe coated fullerene; (d) removing at least a portion of the layer ofinorganic material in a manner suitable for permitting at least twofullerenes to contact each other to provide at least one spontaneousinterconnect; (e) optionally, allowing at least two fullerenes of aspontaneous interconnect to separate; (f) optionally, allowing at leasttwo fullerenes to contact each other to provide at least one newspontaneous interconnect; and (g) depositing a suitable metal contact atthe site of at least one spontaneous interconnect and/or one newspontaneous interconnect.
 28. The method according to claim 27, whereinthe fullerenes are selected from the group consisting of C₆₀, C₇₂, C₈₄,C₉₆, C₁₀₈, C₁₂₀, single-walled carbon nanotubes (SWNT), multi-walledcarbon nanotubes (MWNT), and combinations thereof.
 29. The methodaccording to claim 28, wherein the fullerenes are single-walled carbonnanotubes (SWNT).
 30. The method according to claim 27, wherein the atleast one inorganic material comprises an inorganic oxide.
 31. Themethod according to claim 30, wherein the inorganic oxide is an oxide ofsilicon.
 32. The method according to claim 27, wherein the fullerene isdispersed by a technique of chemical functionalization or surfactantaddition.
 33. The method according to claim 27, wherein removing the atleast a portion of the layer of inorganic material comprises treatmentwith a suitable etchant.
 34. The method according to claim 27, whereinremoving the at least a portion of the layer of inorganic material iseffective in removing all of the inorganic material.
 35. The methodaccording to claim 27, wherein removing the at least a portion of thelayer of inorganic material in a suitable manner comprises selectivelyremoving inorganic material from the ends of the fullerenes.
 36. Themethod according to claim 27, wherein removing the at least a portion ofthe layer of inorganic material in a suitable manner comprisesselectively removing inorganic material from the central portion of thefullerenes.
 37. The method according to claim 27, wherein separating theat least one spontaneous interconnect comprises treatment with asuitable surfactant.
 38. The method according to claim 27, wherein themethod further comprises testing the coated fullerene interconnectdevices for suitability as electronic devices.
 39. A coated fullereneinterconnect device made according to the method of claim
 27. 40. Acoated fullerene interconnect device comprising: a layer of at least oneinorganic material covering at least a portion of at least one surfaceof fullerenes, wherein at least two fullerenes are contacting each otherto form a spontaneous interconnect; and at least one suitable metalcontact is found at the site of at least one spontaneous interconnect.41. The coated fullerene interconnect device according to claim 40,wherein the device performs some electronic switching function.
 42. Thecoated fullerene interconnect device according to claim 40, wherein thedevice performs some electronic memory function.
 43. The coatedfullerene interconnect device according to claim 40, wherein the deviceperforms some electronic sensory function.
 44. A method of depositing adielectric onto a silicon computer chip comprising a coated fullerenecomprising: a layer of at least one inorganic material covering at leasta portion of at least one surface of a fullerene onto a computer chip,wherein the method comprises contacting a solution comprising coatedfullerene with at least one region of a computer chip in a mannereffective for depositing a dielectric layer to said region.
 45. Themethod according to claim 44, wherein contacting a solution comprisingcoated fullerene with at least one region of a computer chip in aneffective manner takes place at a temperature no greater than 50° C. 46.The method according to claim 44, wherein the dielectric layer isuniform in thickness.
 47. The method according to claim 44, whereincontacting a solution comprising coated fullerene with at least oneregion of a computer chip in an effective manner comprises effectingcontrol over the void volume.